The invention herein described was made in the course of or under a contract or subcontract thereunder, with the United States Navy.
The present invention relates generally to marine equipment handling systems and more particularly to such systems for lowering and retrieving bulky and heavy objects from ships and other unstable surface platforms.
In oceanographic work it often is necessary to deploy large and bulky objects from surface vessels for purposes of underwater exploration, observation or the like, and subsequently to retrieve the objects to, and sometimes into, the vessel from which deployed. For example, surveilance sonar systems may employ sonar transducer arrays which are very large in size and very substantial in weight, of the order of many thousands of pounds. Such arrays may conveniently be tethered by a single support line even to a relatively unstable surface platform such as a ship, during deployment and normal operation of the array at depth. During deployment the cable may be paid out sufficiently freely that even abrupt relative motion between the ship and array will not unduly load the cable, and when the array is at its operating depth which typically may be some thousands of feet, the inherent resilience of such long length of cable will permit heaving and other ship motion with respect to the array without excessive loading of the cable and without transmittal of sufficient force loading to the array as to cause it to attempt to follow the ship motion.
During retrieval of such arrays, however, several problems arise. As the array is hoisted upwardly into close proximity with the ship, the short length of cable remaining between the ship and array has too little resilience to permit any substantial relative motion between them, and the array accordingly is constrained to attempt to follow vertical motion of the ship. The resultant extreme fluctuations in loading on the cable may well exceed its strength, causing loss of the array. Also, if as is often the case the array is to be winched into engagement with the ship or into a well or hold formed within the ship, it is necessary that the array be placed into and held in proper orientation with respect to the ship at the moment of contact. Use of heavier cable can be of little if any help on this latter problem, of course, and is of limited benefit even with respect to the cable overload problem because generally cable strength can be improved only at the expense of cable weight, and where extremely long lengths of cable are required the cable weight itself may become the major part of the load and thus become the limiting factor.